engine degreaser, and some pressure washer shampoo... funnily enough, halfords do a big 5 litre bottle of the pressure washer stuff, but if i were you, and serious about car washing... i'd invest in a foam lance and some snowfoam or whatever its called... but i dont think halfords sell that shizzle, but tey do the foam lances, but they are eeeexxxxpensiiiive!
happy days, enjoy yourself!